Positron Emission Tomography (PET) is a highly sensitive imaging modality that is particularly useful for the detection of cancerous tumors using [18F]-FDG. Unfortunately, the extremely high cost and limited axial field of view of current systems have been major obstacles in its clinical application. A whole body PET detector is proposed based on close packed arrays of lead walled straw proportional detectors oriented longitudinally in an annular ring. This approach can bring about a 5 to 10 fold reduction of cost while improving imaging characteristics, such as overall sensitivity and spatial resolution. Using these tubes, an overall 3-D spatial resolution of <5 mm and dead times in the 50 nsec range have been achieved. Furthermore, since straws can be constructed in lengths of 50+ cm, the axial field of view can be greatly increased. Under Phase II, two fully functional 5,000 tube prototype detectors will be constructed using a modular design based on removable 64 to 256 tube units. Each module will have a high speed electronics readout board which will perform coincidence logic, longitudinal position measurement, and identification of straw number and will then transmit this information to a storage system via a digital data bus. The two detectors, complete with readout boards, will be operated in coincidence and will be tested for performance characteristics. Finally, since the increased axial field of view substantially increases the angular acceptance, full 3D reconstruction algorithms will be developed and implemented for image reconstruction. This project will provide proof of principle of a commercial whole body 3-D PET camera with exceptionally high sensitivity, increased axial field of view, and greatly reduced cost. By substantially increasing the practical clinical application of PET, such a system can have a huge impact on metastatic tumor imaging and management of cancer patients. PROPOSED COMMERCIAL APPLICATION: Positron Emission Tomography (PET) is well-established as the most advanced technique for imaging metabolic processes, blood flow, and cancerous tumors. It has substantial diagnostic and research applications in neurology, oncology, and cardiology. Its high cost, however, has prevented its widespread application. A low cost PET camera would allow greater application for this imaging technique and could compete with the current SPECT camera market. The proposed whole body system would also have a large market in the oncology field.